Dehydration in Adults

8 Interesting Facts of Dehydration in Adults 

  1. Dehydration is a term that refers to a reduction in total body water without a proportional reduction in sodium and potassium
  2. Dehydration (loss of free water) is distinct from volume depletion
  3. Most cases are caused by pure water losses from diabetes insipidus, insensible and sweat losses, osmotic diarrhea, or osmotic diureses
  4. Patients who cannot sense thirst or who are unable to access water independently are at greatest risk
  5. One potential major biochemical correlation of hypertonicity from dehydration is hypernatremia
    • Determining acuity (acute versus chronic) and calculating water deficit are both required to devise a fluid repletion protocol
      • Treatment of acute hypernatremia involves rapid replacement of free water within 24 hours, whereas replacement of water deficit should occur slowly in cases of chronic hypernatremia
        • In both cases, 5% dextrose in water IV is the ideal fluid infusion, provided that the patient is volume replete
  6. Monitoring serum sodium concentrations at frequent intervals is required early in the replacement regimen to avoid overly rapid correction, which can lead to adverse neurologic sequelae
  7. Measures to prevent dehydration are important for patients with adipsic diabetes insipidus and for elderly adults in nursing or assisted living facilities
    • Such measures include regular monitoring of body weight with fixed fluid regimens, assistance with and encouragement of drinking beverages, frequent prompting to imbibe fluids, and use of modified drinking cups
  8. Mortality of patients with dehydration is high if not treated adequately and in some studies of elderly patients, approaches 50% 

Pitfalls

  • Pure water deficits do not significantly alter blood volume or GFR, but hypertonicity and hypernatremia can ensue 
  • Except in cases of circulatory collapse, 0.9% sodium chloride (isotonic saline) is unsuitable for managing hypernatremia 
  • Use extreme caution to avoid excessively rapid correction of hypernatremia, which increases risk of iatrogenic cerebral edema
  • Dehydration refers to a reduction in total body water without a proportional reduction in sodium and potassium
    • Classically, the fluid loss of dehydration is predominantly water loss (with little or no sodium or potassium) from the intracellular compartment
    • Loss of free water in dehydration causes an increase in plasma tonicity 
    • Hypertonicity implies a physiologic process of intracellular volume contraction 
  • Dehydration (loss of free water) is distinct from volume depletion
    • Volume depletion refers to the physiologic process of a decrease in extracellular fluid 
    • Volume depletion is a disorder of blood volume contraction and involves a more balanced loss of sodium, potassium, and water
  • Dehydration and volume depletion are not the same, although they can exist concurrently
  • One potential major biochemical correlation of hypertonicity from dehydration is hypernatremia; however, hypernatremia generally only occurs when dehydration is associated with thirst defects or lack of access to water 
  • The American Medical Association proposed that no absolute definition of dehydration exists and that the signs and symptoms of dehydration may be vague, deceptive, or even absent in older adults 

Clinical Presentation

History

  • Symptoms of pure water loss reflect cellular responses to hypertonicity
    • Symptoms of mild dehydration include thirst and fatigue
    • Symptoms that may occur with greater water deficits and increasing hypertonicity—particularly if there is a lack of access to water or in the presence of hypodipsia or adipsia—include lethargy, irritability, confusion, and disorientation 
      • Symptoms may be diminished if hypertonicity develops slowly, allowing brain and neuronal adaptation to maintain cell volume
  • Other important history to elicit or circumstances to consider
    • Presence of hypodipsia or adipsia, as might occur in adipsic diabetes insipidus
    • Reporting of polyuria, also occurring in diabetes insipidus
    • Inability to seek out or access water, perhaps due to impaired mental status or physical constraints
    • Excessive sweating from intense or long-duration exercise, residing in an area with high external temperature, or having a fever
    • Reporting of diarrhea
    • Current hyperglycemia from uncontrolled diabetes, leading to an osmotic diuresis

Physical examination

  • Signs of hypovolemia are usually absent; these technically only occur with combined water and electrolyte losses, which does not fit the strict definition of dehydration
  • Neurologic manifestations occur in the presence of hypertonicity
    • Impaired mental status is a common finding in elderly patients who have water losses and cannot seek replacement on their own
    • On rare occasions, these could include obtundation, coma, and seizures
  • Cardiovascular manifestations (only with concurrent volume loss or with extraordinary pure water losses producing a serum sodium concentration greater than 160 mEq/L) 
    • Orthostatic hypotension
    • Tachycardia
  • Fever, particularly in patients who have difficulty or are completely unable to access water independently (ie, ventilated patient)

Causes

  • Physiology background
    • Body fluid compartments
      • Total volume of water in the human body is about 45% to 60% of body weight under normal conditions 
      • Total body water is divided into an intracellular fluid compartment (two-thirds) and extracellular fluid compartment (one-third)
        • Extracellular fluid is made up of plasma and interstitial fluid
    • Volume depletion refers to loss of extracellular fluid, which also affects intravascular and interstitial compartments
  • Dehydration (loss of body water without sodium) results when water losses from the body exceed water replacement
    • In dehydration, reduction in total body water (mostly) occurs from the intracellular compartment
  • Pure water losses (or maximally hypotonic fluid losses) are potentially caused by several conditions, including:
    • Diabetes insipidus
      • A spectrum of diseases that displays hypotonic polyuria and inability to concentrate urine, owing to inadequate secretion of or impaired renal responsiveness to arginine vasopressin
      • Central diabetes insipidus is caused by hypothalamic and pituitary disorders that impair synthesis or secretion of arginine vasopressin
        • Examples include structural lesions such as mass effect from suprasellar pituitary adenomas, damage from traumatic brain injury, or iatrogenic brain injury from neurosurgery
        • Hypothalamic lesions that cause diabetes insipidus plus thirst defects result in dilute polyuria; additionally, these lesions place patients at high risk of unreplaced water loss 
          • Examples include cases of clipping of anterior communicating artery aneurysm after subarachnoid hemorrhage and craniopharyngioma
      • Nephrogenic diabetes insipidus is caused by various disorders that display renal resistance to arginine vasopressin
        • Some are genetically based and present in infancy
        • Acquired forms are often caused by a variety of medications (eg, lithium)
    • Insensible and sweat losses
    • Osmotic (nonsecretory) diarrhea
    • Osmotic diuresis
      • Glucosuria in uncontrolled diabetes (severe hyperglycemia, as might occur in hyperosmolar hyperglycemic state)
      • Urea from high-protein tube feedings
      • Mannitol, given to reduce intracranial pressure and treat cerebral edema
  • Loss of intestinal secretions that have sodium plus potassium concentrations lower than plasma (as might occur in osmotic diarrhea) can cause hypernatremia; technically, this does not fit the strict definition of pure or “electrolyte” free water losses

Risk factors and/or associations

Age
  • Elderly patients are at risk owing to impaired mental status and diminished stimulation of thirst
    • Thirst perception declines, on average, among older adults
    • Results of an NHANES (National Health and Nutrition Examination Survey) III study of community-dwelling elderly adults found that 28.4% had a plasma osmolality greater than 300 mmol/L and another 39.8% between 295 and 300 mmol/L 
Other risk factors/associations
  • Patient groups at risk for developing dehydration
    • Mechanically ventilated patients
    • Those with altered mental status or inability to access water at will
    • Patients with uncontrolled diabetes and episodes of severe hyperglycemia
    • Athletes participating in endurance events
  • Use of high-protein tube feedings (urea)
  • Environmental factors (eg, high air temperatures)

Diagnostic Procedures

Primary diagnostic tools

  • Diagnosis of dehydration is often made on a presumptive basis using a combination of features
    • No single measure has proved to be the gold standard in diagnosing dehydration
    • Single symptoms, signs, or individual laboratory test results are neither sufficiently sensitive nor specific to indicate a state of dehydration
      • A Cochrane systematic review that examined ability of diagnostic tests to identify older adults with dehydration found that there was limited evidence of the diagnostic utility for any individual clinical symptom, sign, or test to correctly indicate a state of water-loss dehydration 
    • A combination of clinical context and biochemical findings of high serum tonicity with high serum sodium concentrations are suggestive of a state of dehydration 
  • Further laboratory evaluation aims to establish severity of dehydration and assists in the management of replacing water deficit
    • Standard tests include basic metabolic panel
    • Further testing may be required in patients with hypernatremia, particularly when cause is unclear; these tests include serum osmolality, urine osmolality, and urine sodium concentration
  • Additional diagnostic testing may be warranted to ascertain the underlying cause if not apparent by history, clinical context, and physical examination
    • Examples include water deprivation test to assess for adult-onset or previously undiscovered diabetes insipidus or evaluation for osmotic diarrhea

Laboratory

  • Serum chemistry
    • BUN may be slightly elevated with dehydration (hypertonicity), and creatinine will be mostly unchanged
    • Hypernatremia is defined as a rise in the serum sodium concentration exceeding 145 mEq/L 
      • Severe hypernatremia: greater than 150 mEq/L 
    • Hypernatremia may occur in patients with water deficit who are unable to replace water losses owing to thirst defects or an inability to access water
      • Groups at highest risk are infants and patients who have altered mental status, are intubated, and are elderly
      • Generally, hypernatremia will not develop when water losses occur in patients with intact thirst mechanisms and ready access to and ability to drink water
    • Severe hyperglycemia, in the context of the known underlying condition of diabetes mellitus, may indicate an osmotic diuresis
  • Serum and urine osmolality
    • Serum osmolality of 295 mOsm/kg or higher is observed in states of dehydration 
    • Urine osmolality varies, depending on cause; it is low (less than 300 mOsm/kg) in diabetes insipidus
    • Urine osmolality is higher than serum osmolality in states of dehydration caused by fluid loss from skin or gastrointestinal tract
  • Urine sodium concentration
    • Lower than 20 mEq/L in states of hypotonic fluid losses due to gastrointestinal losses, burns, or fever 
    • Greater than 20 mEq/L in states of water loss from enteral feeding, osmotic diuresis, or hyperglycemia 
    • Greater than 100 mEq/L in states of sodium loading (oral ingestion or IV) 
  • Urine specific gravity
    • May be elevated in many patients with dehydration but is often inaccurate as a test indicating hydration status 

Differential Diagnosis

Most common

  • Volume depletion
    • Dehydration and volume depletion are often used interchangeably but technically represent different pathophysiologic conditions
    • Volume depletion refers to a deficit in extracellular fluid volume, producing blood volume contraction
    • Volume depletion results from loss of both sodium and water from gastrointestinal, renal, and cutaneous sites
      • Common scenarios include vomiting, diarrhea, gastrointestinal bleeds, gastrointestinal drains, diuretic use, sweat, and burns
      • In some conditions (eg, acute pancreatitis, peritonitis, intestinal obstruction), volume depletion occurs when interstitial and intravascular fluid moves into third spacing
    • Volume depletion is a clinical diagnosis supported by laboratory studies
    • Symptoms of volume depletion include those that are due to hypovolemia itself (as a result of hemodynamic effects of reduced intravascular volume) and those that are related to the underlying cause
      • Symptoms of volume depletion due to hypovolemia include fatigue, thirst, and dizziness
      • Symptoms related to the underlying cause could include vomiting, diarrhea, or symptoms of skin burns
    • Signs of volume depletion include those that are due to the hypovolemia itself and those related to the underlying cause
      • Signs of volume depletion due to hypovolemia include postural hypotension, tachycardia, decreased skin turgor, and low urine output
        • Orthostatic changes in blood pressure do not become evident in healthy patients until an acute blood volume deficit of 15% to 20% occurs 
        • Orthostatic changes only rarely occur with pure water losses
        • Pure water losses are more likely to lead to hypernatremia and hypertonicity
      • Symptoms or signs of volume depletion due to the related underlying cause
        • Diarrhea, from gastroenteritis
        • Polyuria, from diuretics
    • Laboratory studies in volume depletion will show markedly increased BUN and rise in serum creatinine concentration, as well as hemoconcentration 
      • In hypertonicity and water losses, BUN is modestly elevated, there is little to no change in serum creatinine concentration, and no hemoconcentration 
  • Hypernatremia due to sodium overload
    • Administration of hypertonic saline or oral ingestion of a large amount of sodium salts can cause hypernatremia
    • Hypertonic saline, when given to treat a variety of conditions (eg, irrigation of hydatid cysts, saline solutions to induce abortion), may raise serum sodium concentration in the absence of water losses
    • Differentiate from dehydration based on clinical context

Treatment Goals

  • Replace water deficit
  • Treat the process that represents any underlying cause

Disposition

Admission criteria

Inpatient hospitalization is required when replacing water deficits with IV fluids owing to frequent monitoring of serum sodium concentrations

Criteria for ICU admission
  • Impending circulatory collapse for patients with both dehydration and volume depletion

Recommendations for specialist referral

  • Consult nephrologist or endocrinologist for evaluation and management of complex cases of dehydration associated with hypernatremia (eg, those due to suspected or known diabetes insipidus)

Treatment Options

Treatment of dehydration depends on acuity or severity of condition and underlying cause

For urgent treatment of severe hypernatremia associated with dehydration (serum sodium concentration greater than 150 mEq/L), initiate replacement of free water 

  • Work-up of underlying cause may need to be delayed in severe cases

Steps involved in replacement of free water

  • First, for patients with hypernatremia, calculate water deficit
    • Water deficit = total body water × [(serum sodium concentration / 140) − 1] 
      • Total body water is an estimate that is approximately 60% lean body weight in young men, 50% lean body weight in young women, 50% lean body weight in older men, and 45% lean body weight in older women 
    • Caveat 1: serum sodium concentration must be corrected for hyperglycemia, using the following formula:
      • Corrected serum sodium = measured serum sodium concentration + [1.7 × Δ(glucose in mg/dL) / 100] 
        • For every 100 mg/dL increase in serum glucose, there is a 1.7 mEq/L decrease in serum sodium concentration 
    • Caveat 2: calculated water deficit estimates water balance that must be replaced to lower serum sodium concentration to reference range; however, ongoing free water losses are not included in this calculation and, if significant (ie, in large urinary or gastrointestinal losses), they must be added to this equation
  • To replace water in chronic (lasting longer than 48 hours) hypernatremia or hypernatremia of unknown duration
    • Correct slowly, over about 48 hours
      • Goal is to slowly reduce serum sodium concentration by 10 to 12 mEq/L over the first 24 hours, with correction of entire water deficit over 48 hours or more 
      • Rapid rehydration of hypernatremia can cause cellular swelling and rupture with consequent cerebral edema
    • Administer 5% dextrose in water IV based on free water deficit (ie, at an approximate rate of 1.35 mL/hour × patient weight in kg) 
      • Add ongoing water losses if these are occurring and can be estimated
    • If patient is stable and conscious, orally rehydrate with water
    • In cases where both volume depletion and hypernatremia are present, restore intravascular volume with isotonic sodium chloride before administering free water 
  • To replace water in acute (lasting less than 24 hours) hypernatremia
    • Correct entire water deficit quickly, in less than 24 hours 
    • Administer 5% dextrose in water IV at an approximate rate of 3 to 6 mL/kg/hour 
      • Add any ongoing water losses if they can be estimated
    • Goal is to reduce serum sodium concentration by 1 to 2 mEq/L per hour and achieve a serum sodium concentration within reference limits in less than 24 hours 
  • Other considerations
    • If hypernatremia is accompanied by hyperglycemia with diabetes, treatment of hyperglycemia with insulin is required to provide free water in dextrose solution
      • Other tactics to mitigate glycosuria include using a slower rate of 5% dextrose in water infusion, or reducing the dextrose concentration to 2.5%
    • If water deficit is small and patient is alert, oral correction is acceptable and often preferred
    • If the patient has known central diabetes insipidus, it is crucial to consult an endocrinologist to manage desmopressin administration
  • Monitoring
    • Monitor serum sodium concentration every 1 to 2 hours initially while administering 5% dextrose in water IV to ensure appropriate rate of fall; can extend interval to every 4 hours, then every 6 hours once target rate of correction has been attained
    • If rate of correction is too slow, as might occur with ongoing losses, increase infusion rate
    • If rate of correction is too rapid, slow infusion rate
    • Monitor serum glucose because some patients will become hyperglycemic when given IV dextrose

Underlying cause of water deficit

  • Managing underlying condition is necessary to reverse metabolic defect and, secondarily, to prevent further episodes. May require 1 of several measures, including: 
    • Attenuating gastrointestinal fluid losses
    • Initiating or optimizing desmopressin therapy
    • Controlling pyrexia, reversing hyperglycemia, and reducing glucosuria
    • Withholding diuretics
    • Discontinuing culprit medications

Nondrug and supportive care

Special populations

  • Patients in hyperosmolar hyperglycemic state
    • Frequently, dehydration and volume depletion coexist
      • Free water with electrolytes and glucose is lost via urinary excretion, producing glycosuria and causing moderate to severe dehydration
      • Dehydration is usually severe in hyperosmolar hyperglycemic state, even greater than in DKA, and there is risk for cardiovascular collapse
    • Treatment of fluid losses requires addressing 3 issues simultaneously: restoring circulating blood volume; replacing extracellular fluid deficits and lessening hyperglycemia; and correcting free water losses
      • First, treat volume depletion in these patients with a bolus of 0.9% normal saline IV (usually 1-1.5 L over 1-2 hours), followed by an ongoing infusion of 0.9% or 0.45% normal saline IV depending upon the corrected serum sodium concentration 
      • Start IV insulin infusion after initiating IV fluids 
      • Once hemodynamic parameters have stabilized, IV fluids may need to be switched to 0.45% normal saline (if the serum sodium concentration is within reference limits or high) or to 0.9% normal saline (if the serum sodium concentration is low) 
      • When glucose levels reach 200 to 250 mg/dL, switch to 5% dextrose in water IV to begin free water correction and to reduce hyperosmolality 
      • Managing other aspects of hyperosmolar hyperglycemic state (eg, nuances of treating hyperglycemia and evaluation to determine precipitant) is complex and can require consultation of endocrinologist, nephrologist, and/or hospital intensivists
  • Patients with acute kidney injury
    • For patients with concomitant renal disease, treatment of hypernatremia may require hemodialysis or continuous renal replacement therapy 

Monitoring

  • Reassess fluid prescription at regular intervals, taking into account laboratory values and patient’s clinical status 
  • Monitor serum sodium concentration every 1 to 2 hours initially while administering 5% dextrose in water IV; extend interval to every 4 hours, then every 6 hours, then every 12 hours provided that desired rate of sodium lowering is achieved
  • Continue monitoring until sodium concentration has returned to reference range

Complications

  • Hypernatremia is a major biochemical manifestation of dehydration, and complications of this metabolic abnormality (if untreated), include: 
    • Intracerebral and subarachnoid hemorrhages
    • Seizures
    • Coma
    • Death (particularly with sodium concentrations greater than 180 mEq/L) 
    • Osmotic demyelination due to overly rapid correction

Prognosis

  • Often varies with underlying cause
  • Dehydration alone
    • Mortality of patients with dehydration is high if not treated adequately and, in some studies of elderly patients, approaches 50% 
    • Elderly patients with dehydration are at risk of developing confusion and show impaired cognitive function 
  • Dehydration when associated with hypernatremia
    • Rapid changes in serum sodium concentrations in either direction can cause severe, permanent, and sometimes lethal brain injury due to osmotic demyelination 
    • If severe hypernatremia develops over a period of minutes (eg, after massive ingestion of salt that may occur in a suicide attempt), vascular injury created by a suddenly shrinking brain causes intracranial hemorrhage 
    • Mortality rate associated with hypernatremia varies according to severity of condition and rapidity of onset. It is often difficult to determine the sole contribution of hypernatremia to mortality from the contribution of underlying or comorbid illnesses 
      • Mortality rates of patients with hypernatremia reported in the literature range from 42% to 60% 
    • Cases of hypernatremia associated with adipsic diabetes insipidus are associated with a mortality rate of about 25%, thought to be caused by a propensity for marked changes in sodium concentrations 

Prevention

  • Adequate intake of total water prevents deleterious, primarily acute, effects of dehydration, which include metabolic and functional abnormalities
  • Ranges for normal intake are wide, and daily consumption above or below those ranges may still be compatible with normal hydration
    • Physically active patients or those who are exposed to hot environments require higher intakes of total water
  • Median adequate intake for total water, as determined in young adults
    • Young men (ages 19-30 years): 3.7 L/day, with fluids providing 3 L/day 
    • Young women (ages 19-30 years): 2.7 L/day, with fluids providing 2.2 L/day 
  • Measures to prevent dehydration in institutionalized elderly patients include: 
    • Increasing staff awareness of the prevalence of the problem
    • Increasing staff assistance with drinking and toileting
    • Providing greater choice and availability of beverages
    • Offering fluids regularly, verbal prompting, and providing straws and modified cups
  • Prevention of dehydration for patients with adipsic diabetes insipidus involves several measures including:
    • Strict adherence to pharmacotherapy (desmopressin)
    • Regular (eg, daily) monitoring of body weight
    • Careful patient adherence to water intake schedules that are based on body weight measurements
    • Periodic measurements of serum sodium concentrations

References

Mahowald JM et al: Hypernatremia in the elderly: relation to infection and mortality. J Am Geriatr Soc. 29(4):177-80, 1981

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